The present invention relates to a method for determining the organic carbon content of raw mineral materials, e.g., crushed raw rocks and the like. The present invention is more particularly concerned with a method for determining in a short period of time the organic carbon content by using a small amount sample of the raw material and to an apparatus for performing such a determination.
The determination of the organic carbon content in mineral materials has a wide field of practical applications. It is very convenient to evaluate the geological sediments from samples which may be carried on the surface of the ground, in a drilling well, on drill cuttings or on drilling cores.
One of the most important geochemical parameters to evaluate for an oil drilling certainly is the amount of available organic matter, including both soluble and insoluble organic components. The organic carbon content of a kerogen rock, which represents the insoluble organic matter closely associated to this rock, should advantageously be determined and made visible with a diagraph on the very site of an oil drilling.
Up to now, the organic carbon content has always been determined according to a very time consuming method which requires previous physico-chemical treatment of the sediments, and especially an extraction by a solvent and an acid treatment to eliminate the carbonates. The sample is then submitted to a pyrolysis in the presence of a catalyst and the amount of CO.sub.2 which is formed from the organic matter is determined. It is obvious that with such a method, the carbonates present in the rock must be completely eliminated, because they also emit some CO.sub.2 which is not representative of the organic carbon content of the rock. The time which is needed for these various operations is at least one day, and the advantage of a method allowing determination of the organic carbon content in a short period of time is easily understood.
A method for determining the carbonic gas content of geological sediments, which have not been submitted to any physico-chemical treatments, has already been proposed. This method comprises carrying out the pyrolysis of the sediments within narrowly defined temperature limits, namely between 150.degree. and 400.degree. C. This determination method for the carbonic gas in untreated samples is not suitable to determine the organic carbon content. It only gives indications on the state of diagenesis of the matter, because the determination of the carbonic gas emitted does not allow to establish a correlation with the organic total carbon content of the matter.